1. Field of the Invention
The invention relates to a process and a device for rapid switching of digital television programs.
2. Description of the Related Art
With the advent, some years ago, of digital television, the viewer's habits are undergoing changes. After having assimilated the concept of a pay-per-view station, he is now offered access to several tens of programs by setting up satellite reception. The label “digital” associated with this new technology reassures the consumer. For the public at large, and especially since the advent of the Compact Disc, “digital” has become synonymous with “quality”.
However, the potential purchaser of digital equipment is not necessarily aware of certain constraints related to this new system. Certain functionalities of his present equipment are no longer possible with satellite reception, such as displaying a program and recording another one at the same time. He also has to wait several seconds to go from one program to another.
Indeed, when the viewer indicates, with the aid of his remote control, that he wishes to change program, the digital decoder must carry out a number of operations which are the consequence of this idle time:                take the request into account:        direct taking into account of the number of the program or increment/decrement of the number of the program in progress        calculate the parameters of the program:        modulation frequency, program identifier (PID standing for Packet IDentifier) . . .        dispatch a signal to the LNB block (the acronym standing for Low Noise Block) for satellite reception:        this signal indicates the demodulation frequency band (from 10.75 GHz to 11.70 GHz or 11.70 GHz to 12.70 GHz)        return from the satellite reception of the correct frequency band:        the demodulation frequency has been lowered so as to lie between 950 MHz and 2150 MHz        demodulation at decoder level of the frequency of the intended channel        digital demodulation of the signal        filtering of the PIDs        awaiting the first image of intra type        (definition given in the MPEG standard)        video decoding and synchronization with the audio        output by the decoder of the signal decoded and dispatched to the monitor.        
The stringing together of all these operations gives rise to an idle time, resulting in a black image or an image which is frozen on the screen for around 2 to 3 seconds. This annoyance precludes fast perusal of the offerings of a package of programs.